The verteron array was powerful energy-producing device based on Mars, designed to redirect comets in the Sol System via verteron pulses towards the polar ice caps on Mars, for the purpose of terraforming the planet.
The array was hijacked by John Frederick Paxton, leader of the xenophobic group Terra Prime, who used it to further his cause of Human superiority. Using the array to fire on Earth's moon Luna as a demonstration of its power, Paxton threatened to destroy Star Fleet Command unless all aliens evacuated the solar system. When the Enterprise, NX-01 attempted to stop him, Paxton used the array to fire on Enterprise, critically damaging them.
Eventually, Captain Jonathan Archer was successful in leading a team to infiltrate Paxton's base and stopping him.